1. Field of the Invention
The present invention relates to an electric rotating machine and its (coil) connecting method thereof.
2. Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 11-356015 published on Dec. 24, 1999 exemplifies a previously proposed rotating machine. The previously proposed rotating machine described in the above-described Japanese Patent Application First Publication adopts a three-layer structure of two rotors and a single stator. When a compound current is caused to flow through the rotating machine, a torque developed on one of the rotors can be non-interfered against that developed on the other rotor. The compound current can be realized by adding currents having two different frequencies or having two different phases. At the same time, in the same manner as the compound current, a synthesized voltage like a compound voltage needs to be generated having the two different frequencies or having the two different phases.
A Japanese Patent Application First Publication No. 2001-231227 published on Aug. 24, 2001 (which corresponds to a U.S. patent application Publication No. 2001/0020805 A1 published on Sep. 13, 2001) exemplifies a previously proposed compound motor having stator coils and rotors respectively independently operated of each pair of stator coils and rotors. In the latter previously proposed compound motor, an ineffective current in a case where the coils of the same polarities at two stator coils are connected in parallel to each other is controlled so as to improve an entire efficiency.